About 300,000 years after the Big Bang the Universe was dark, filled mainly with neutral hydrogen gas and with no stars, planets, or galaxies. Over the next half billion years, the first galaxies started to appear, and then sometime between 300 million years and one billion years after the Big Bang a transformative event known as the Epoch of Reionization occurred. During this event, the Universe went from being almost completely neutral to a state in which it became almost completely ionized.

The Epoch of Reionization is linked to many fundamental questions in cosmology and astronomy and is being studied by numerous groups, including the LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization). The LAGER project utilises a highly sensitive camera and telescope to search for galaxies that occurred before reionization. Galaxies that were formed before the Epoch are­ difficult to detect, as the large clouds of hydrogen gas scatter the light (like headlights in fog); however, as time progressed more and more galaxies were created, burning up the hydrogen gas and making them easier to detect. By searching for these early galaxies at the distant reaches of the Universe, the LAGER team are effectively looking back in time to try and see which galaxies formed before the Epoch and which formed afterwards, thereby helping to pinpoint the exact time that reionization occurred. The first results of the survey imply that a large fraction of these first illuminating galaxies formed less than 800 million years after the Big Bang, and the next stage of the research will be to continue to search the night sky for these early galaxies, to better determine the Epoch of Reionization.